// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef IPC_IPC_MESSAGE_ATTACHMENT_SET_H_
#define IPC_IPC_MESSAGE_ATTACHMENT_SET_H_

#include <stddef.h>

#include <vector>

#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "build/build_config.h"
#include "ipc/ipc_export.h"

#if defined(OS_POSIX)
#include "base/files/file.h"
#endif

namespace IPC {

class BrokerableAttachment;
class MessageAttachment;

// -----------------------------------------------------------------------------
// A MessageAttachmentSet is an ordered set of MessageAttachment objects
// associated with an IPC message. There are three types of MessageAttachments:
//   1) TYPE_PLATFORM_FILE is transmitted over the Channel's underlying
//   UNIX domain socket
//   2) TYPE_MOJO_HANDLE is transmitted over the Mojo MessagePipe.
//   3) TYPE_BROKERABLE_ATTACHMENT is transmitted by the Attachment Broker.
// Any given IPC Message can have attachments of type (1) or (2), but not both.
// These are stored in |attachments_|. Attachments of type (3) are stored in
// |brokerable_attachments_|.
//
// To produce a deterministic ordering, all attachments in |attachments_| are
// considered to come before those in |brokerable_attachments_|. These
// attachments are transmitted across different communication channels, and
// multiplexed by the receiver, so ordering between them cannot be guaranteed.
//
// -----------------------------------------------------------------------------
class IPC_EXPORT MessageAttachmentSet
    : public base::RefCountedThreadSafe<MessageAttachmentSet> {
public:
    MessageAttachmentSet();

    // Return the number of attachments
    unsigned size() const;
    // Return the number of file descriptors
    unsigned num_descriptors() const;
    // Return the number of mojo handles in the attachment set
    unsigned num_mojo_handles() const;
    // Return the number of brokerable attachments in the attachment set.
    unsigned num_brokerable_attachments() const;
    // Return the number of non-brokerable attachments in the attachment set.
    unsigned num_non_brokerable_attachments() const;

    // Return true if no unconsumed descriptors remain
    bool empty() const { return 0 == size(); }

    // Returns whether the attachment was successfully added.
    // |index| is an output variable. On success, it contains the index of the
    // newly added attachment.
    // |brokerable| is an output variable. On success, it describes which vector
    // the attachment was added to.
    bool AddAttachment(scoped_refptr<MessageAttachment> attachment,
        size_t* index,
        bool* brokerable);

    // Similar to the above method, but without output variables.
    bool AddAttachment(scoped_refptr<MessageAttachment> attachment);

    // Take the nth non-brokerable attachment from the beginning of the vector,
    // Code using this /must/ access the attachments in order, and must do it at
    // most once.
    //
    // This interface is designed for the deserialising code as it doesn't
    // support close flags.
    //   returns: an attachment, or nullptr on error
    scoped_refptr<MessageAttachment> GetNonBrokerableAttachmentAt(unsigned index);

    // Similar to GetNonBrokerableAttachmentAt, but there are no ordering
    // requirements.
    scoped_refptr<MessageAttachment> GetBrokerableAttachmentAt(unsigned index);

    // This must be called after transmitting the descriptors returned by
    // PeekDescriptors. It marks all the non-brokerable descriptors as consumed
    // and closes those which are auto-close.
    void CommitAllDescriptors();

    // Returns a vector of all brokerable attachments.
    std::vector<scoped_refptr<IPC::BrokerableAttachment>>
    GetBrokerableAttachments() const;

    // Replaces a placeholder brokerable attachment with |attachment|, matching
    // them by their id.
    void ReplacePlaceholderWithAttachment(
        const scoped_refptr<BrokerableAttachment>& attachment);

#if defined(OS_POSIX)
    // This is the maximum number of descriptors per message. We need to know this
    // because the control message kernel interface has to be given a buffer which
    // is large enough to store all the descriptor numbers. Otherwise the kernel
    // tells us that it truncated the control data and the extra descriptors are
    // lost.
    //
    // In debugging mode, it's a fatal error to try and add more than this number
    // of descriptors to a MessageAttachmentSet.
    static const size_t kMaxDescriptorsPerMessage = 7;

    // ---------------------------------------------------------------------------
    // Interfaces for transmission...

    // Fill an array with file descriptors without 'consuming' them.
    // CommitAllDescriptors must be called after these descriptors have been
    // transmitted.
    //   buffer: (output) a buffer of, at least, size() integers.
    void PeekDescriptors(base::PlatformFile* buffer) const;
    // Returns true if any contained file descriptors appear to be handles to a
    // directory.
    bool ContainsDirectoryDescriptor() const;
    // Fetch all filedescriptors with the "auto close" property. Used instead of
    // CommitAllDescriptors() when closing must be handled manually.
    void ReleaseFDsToClose(std::vector<base::PlatformFile>* fds);

    // ---------------------------------------------------------------------------

    // ---------------------------------------------------------------------------
    // Interfaces for receiving...

    // Set the contents of the set from the given buffer. This set must be empty
    // before calling. The auto-close flag is set on all the descriptors so that
    // unconsumed descriptors are closed on destruction.
    void AddDescriptorsToOwn(const base::PlatformFile* buffer, unsigned count);

#endif // OS_POSIX

    // ---------------------------------------------------------------------------

private:
    friend class base::RefCountedThreadSafe<MessageAttachmentSet>;

    ~MessageAttachmentSet();

    // All elements either have type TYPE_PLATFORM_FILE or TYPE_MOJO_HANDLE.
    std::vector<scoped_refptr<MessageAttachment>> attachments_;

    // All elements have type TYPE_BROKERABLE_ATTACHMENT.
    std::vector<scoped_refptr<BrokerableAttachment>> brokerable_attachments_;

    // This contains the index of the next descriptor which should be consumed.
    // It's used in a couple of ways. Firstly, at destruction we can check that
    // all the descriptors have been read (with GetNthDescriptor). Secondly, we
    // can check that they are read in order.
    mutable unsigned consumed_descriptor_highwater_;

    DISALLOW_COPY_AND_ASSIGN(MessageAttachmentSet);
};

} // namespace IPC

#endif // IPC_IPC_MESSAGE_ATTACHMENT_SET_H_
